Slag is a by-product generated in iron-making and steel-making processes. Slag is necessarily produced from gangues of cokes or iron ores in iron-making processes, or oxides produced during oxidation and reduction processes of molten iron or molten steel or from other additives in steel-making processes.
Slag comprises SiO2 and CaO, and may also include Al2O3, FeO, MgO, P2O5 and CaS depending on the type of refining reaction.
Iron slag is comprises CaO—SiO2—Al2O3, and steel slag based on oxidation of molten iron or molten steel comprises CaO—SiO2—FeO.